The aim of this work is to characterize the effects of hygrothermal aging in the plain strain fracture toughness of the epoxy system composed by cycloaliphatic epoxy resin and diglycidyl ether of bisphenol-A (DGEBA). For this, after having been under hygrothermal aging in a climatic chamber, epoxy samples were studied using ASTM D5045 fracture toughness test, and micrography and roughness measurements of the fracture surface. It is reported a rapid decrease of GIc and KIc during the first 2 days. Moreover, a numerical model [13] was used to simulate and see with more detail the water absorption in the aged samples. From that, it was observed the heterogeneous distribution of water. Accordingly, it was proposed that the results should be correlated with the water content at the vicinity of the crack tip. Consequently, it was possible to obtain, by quasi-static simulations, the ideal load-displacement curves of crack propagation in the heterogeneous samples. Finally, another contribution of this work is the study of the fracture surface, that gives a clue of the relationship among the fracture energy, the appearance of microcracks in the fracture surface, and the roughness (Ra).

Submitted by Stefhany Costa Barbizan null (stefhanybarbizam@hotmail.com) on 2018-01-24T15:50:22Z No. of bitstreams: 1 DISS 2018.pdf: 9636418 bytes, checksum: 4d62ecb173fdcea62201fab783a6dfc1 (MD5) / Approved for entry into archive by Silvana Alvarez null (silvana@ict.unesp.br) on 2018-01-24T16:32:32Z (GMT) No. of bitstreams: 1 Astuti_scb_me_sjc.pdf: 9405812 bytes, checksum: 099df02868bd44f2c4a02f03b5a2e97f (MD5) / Made available in DSpace on 2018-01-24T16:32:32Z (GMT). No. of bitstreams: 1 Astuti_scb_me_sjc.pdf: 9405812 bytes, checksum: 099df02868bd44f2c4a02f03b5a2e97f (MD5) Previous issue date: 2017-12-14 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A literatura mostra escassez de informações sobre o envelhecimento de cerâmicas Y-TZP de uso odontológico, quando associado a escovação simulada. Sendo assim, o objetivo deste estudo foi avaliar o efeito da escovação simulada em algumas propriedades de zircônias estabilizadas por ítria (Y-TZP) após envelhecimento hidrotérmico. Foram confeccionados 36 discos da cerâmica (YZ®) – ISO 6872, 36 da cerâmica Cercon®Zirconia (DENTSPLY Ceramco, EUA) e 36 discos da cerâmica (Zirkon Transluzent - ICE Zirkonzahn®) os quais foram separados de acordo com o envelhecimento em reator hidrotérmico (controle e 6 horas de envelhecimento) e submissão à ciclagem de escovação simulada (controle e 72000 ciclos com carga de 350g e solução creme dental/água), resultando em 3 grupos de estudo, de acordo com o tipo de cerâmica utilizada para confecção da amostra e 4 Sub grupos, de acordo com a realização ou não do envelhecimento Hidrotérmico e escovação simulada nas amostras (n=9). Sendo YZ- Amostras realizadas com a cerâmica(YZ®);CZ- Amostras realizadas com a cerâmica-(Cercon®Zirconia);ZT- Amostras realizadas com a cerâmica (Zirkon Transluzent - ICE Zirkonzahn®).Teremos como subgrupos, 0- Grupo controle, amostras não submetidas nem ao envelhecimento, nem a escovação simulada; 1- Amostras submetidas apenas ao envelhecimento por 6 horas; 2- Amostras submetidas somente a escovação simulada; 3- Amostras submetidas ao envelhecimento hidrotérmico por 6 horas e escovação simulada. Os corpos de prova foram avaliados por difração de Raio-X para verificar transformação de fase T-M e uma amostra de cada grupo submetida à análise morfológica em microscopia eletrônica de varredura (MEV). As amostras foram submetidas ao teste de flexão biaxial em máquina de ensaios universal, ensaiadas até o momento da fratura e os dados obtidos foram submetidos a análise de variância de dois fatores. Também foi realizado o teste de Tukey (P<0,05), para analisarmos a interação entre o tipo de cerâmica e o tratamento realizado (CxT). As análises nos mostraram que os grupos envelhecidos sofreram maior alteração de fase que os grupos só escovados, e quando os dois procedimentos foram associados, a formação de fase monoclínica foi maior. Além disso, as micrografias mostraram que os grãos de zircônia se expandiram na tentativa de conter um possível defeito estrutural e muitos se soltaram devido a abrasão da escovação. Dessa forma, pode-se concluir que, as análises de DRX e MEV foram essenciais para identificação da alteração de fase sofrida pelas cerâmicas, confirmando o comportamento de desgaste já descrito na literatura, quando submetidas a tratamentos de envelhecimento hidrotérmico. / The literature shows a shortage of information about the aging of Y-TZP ceramics for dental use, when associated with simulated brushing. Therefore, the objective of this study was to evaluate the effect of simulated brushing on some properties of yttria stabilized zirconia (Y-TZP) after hydrothermal aging. Sixteen ceramic discs (YZ®) - ISO 6872, 36 Cercon®Zirconia ceramics (DENTSPLY Ceramco, USA) and 36 ceramic discs (Zirkon Transluzent - ICE Zirkonzahn®) were prepared, which were separated according to the aging in the reactor hydrothermal (control and 6 hours of aging) and submission to simulated brushing cycle (control and 72000 cycles with 350g load and toothpaste / water solution), resulting in 3 study groups, according to the type of ceramics used for cooking of the sample and 4 Sub groups, according to whether or not Hydrothermal aging and simulated brushing were performed in the samples (n = 9). (YZ®); CZ- Samples made with ceramics- (Cercon®Zirconia); ZT- Samples made with ceramics (Zirkon Transluzent - ICE Zirkonzahn®) .We will have as subgroups, 0- Control group, samples not submitted neither to aging nor simulated brushing; 1- Samples submitted only to aging for 6 hours; 2 - Samples submitted only to simulated brushing; 3 - Samples submitted to hydrothermal aging for 6 hours and simulated brushing. The specimens were evaluated by X-ray diffraction to verify T-M phase transformation and a sample of each group submitted to scanning electron microscopy (SEM) morphological analysis. The samples were submitted to the biaxial flexion test in a universal test machine, tested until the moment of fracture and the data obtained were submitted to two-way analysis of variance. The Tukey test (P <0.05) was also used to analyze the interaction between the type of ceramic and the treatment (CxT). The analyzes showed that the aged groups suffered a greater phase change than the groups only brushed, and when the two procedures were associated, the monoclinic phase formation was larger. In addition, the micrographs showed that the zirconia grains expanded in an attempt to contain a possible structural defect, and many were released due to abrasion of the brush. Thus, it can be concluded that the XRD and SEM analyzes were essential for the identification of the phase change suffered by the ceramics, confirming the wear behavior already described in the literature when submitted to hydrothermal aging treatments.

[pt] Materiais à base de zircônia apresentam excelentes propriedades mecânicas, estabilidade química e dimensional, tenacidade, juntamente com um módulo de Young na mesma ordem de grandeza de ligas de aço inoxidável. Devido à essas características, a zircônia tem sido utilizada em uma ampla gama de aplicações, incluindo a fabricação de peças protéticas. As modificações na composição da zircônia e o desenvolvimento do CAD-CAM (computer assisted design) fizeram com que as próteses à base de zircônia se tornassem um procedimento clinico frequentemente realizado na atual Odontologia restauradora. Blocos pré-sinterizados de zircônia, fabricados industrialmente, homogêneos e com falhas mínimas são usinados em um ambiente industrial controlado para receberem a forma desejada. Após a usinagem, as peças em zircônia são sinterizadas para promover sua densificação final. Este processo reduz os possíveis defeitos criados por etapas laboratoriais manuais e intermediárias na confecção de restaurações dentárias. O objetivo deste estudo foi avaliar o efeito da degradação hidrotérmica e do jateamento com óxido de alumínio nas propriedades mecânicas de três tipos de zircônia tetragonal policristalina estabilizada por ítria (ZTPI). Três tipos de zircônias contendo diferentes concentrações de ítria e grau de translucidez foram utilizadas: ZTPI com 5,2 por cento mol (Prettau Anterior Super-Translúcida da Zirkonzahn), ZTPI com 3 por cento mol de Y2O3 (VIPI Block Zirconn) e ZTPI com 3 por cento mol de Y2O3 com translucidez melhorada (VIPI Block Zirconn Translucent). Todas indicadas para uso em próteses odontológicas monolíticas. 15 corpos de prova de cada zircônia testada foram sinterizados e divididos em três grupos de acordo com otratamento de superfície e processo de degradação. No Grupo I as zircônias sofreram jateamento com óxido de alumino. No grupo II as zircônias foram lixadas e polidas. No grupo III as zircônias foram lixadas, polidas, recuperadas e degradadas em reator hidrotérmico por 5 horas a 134 graus Celsius e 2 bar. Para a caracterização microestrutural foram realizados ensaios de difração de raios-X, espectrometria Raman, densidade relativa, microdureza Vickers, rugosidade superficial e análise de tamanho médio de grão por MEV. Os resultados mostraram que a densidade de todos os grupos ficou acima de 99 por cento e que a degradação promoveu a transformação de fase monoclínica e afetou os valores de resistência à flexão. No entanto, a indicação clínica das cerâmicas não foi alterada. O tamanho médio de grão ficou entre 0,367 e 0,621 micrômetros. A dureza e tenacidade à fratura do material não sofreram alterações em função do teor de ítria ou das fases cristalinas presentes. A degradação não afetou de forma significativa os valores de rugosidade, porém, o jateamento com óxido de alumínio não só afetou os valores de flexão como alterou a indicação clínica de cerâmicas utilizadas neste trabalho. / [en] Zirconia-based materials present excellent mechanical properties, tenacity, chemical, and dimensional stability as well as their Young modulus is similar to stainless steel alloys. Due to these characteristics, zirconia has been largely applied in the fabrication of dental prostheses. Modifications in the zirconia composition and the development of CAD-CAM systems has allowed zirconia-based restorations to become a common clinical procedure in current dentistry. Fully sintered and homogeneous blocks from industry are machined at controlled environments seeking to obtain the desired geometry of the restorations. After the machining process, the restorations are sintered to improve their density. This process reduces the failures caused by manual and laboratorial manipulations during fabrication procedure. The aim of this study is to evaluate the effect of hydrothermal aging and sandblasting with aluminum oxide on the mechanical properties of three Yttria-containing tetragonal zirconia polycrystalline (Y-TZP). Three types of Y-TZP, containing different yttria dioxide, were used in the study: Y-TZP with 5,2 per cent mol Y2O3 (Prettau Anterior Super-Translúcida da Zirkonzahn), Y-TZP with 3 per cent mol de Y2O3 (VIPI Block Zirconn) and Y-TZP with 3 per cent mol Y2O3 and optimized translucency (VIPI Block Zirconn Translucent). All the zirconias are indicated for being used as monolithic restorations. 15 specimens from each zirconia tested were sintered and distributed to three groups according to the surface treatment and the aging process. In the group I, the specimens were sandblasted with aluminum oxide particles. For the group II, the zirconia specimens were abraded and polished. In the group III, the specimens were abraded, polished, recovered and aged in a reactor controller for 5 hours at 134 degrees Celsius and 2 bar. The characterization of the zirconia microstructure has been carried out by means of: X-ray diffraction, relative density, Raman spectroscopy, Vickers microhardness, superficial roughness. In addition, the average grain size analysis by scanning electron microscopy were made. The results show that the relative density values were above 99 per cent, and that the hydrothermal aging causes monoclinic phase transformation and affects flexural strength values. However, the clinical indications of materials did not change. The average grain size was between 0.367 and 0.621. The microhardness and tenacity values of materials did not change by yttria concentration or crystallographic phases. The roughness values were not significantly affected by the hydrothermal aging. On the other hand, the flexural strength values were affected by sandblasting process and clinical indication of ceramics tested was changed.

Les normes plus restrictives visent à réduire les émissions de polluants, en particulier le CO2, favorisant l'usage des biocarburants. Cependant, le biodiesel contient des éléments inorganiques (Na, K, Ca et P) qui réduisent la durabilité des systèmes de post-traitement. Dans ce travail sont évalués les performances des catalyseurs d'oxydation diesel (DOCs, catalyseur de référence PtPd/CeZrO2/La-Al2O3). Les résultats de caractérisation ont montré l’influence de ces impuretés sur les propriétés physico-chimiques et catalytiques. Bien que la structure cristalline du catalyseur de référence ne change pas après l'incorporation des impuretés, la surface spécifique diminue. La capacité redox a diminué lorsque les impuretés Na, K et Ca sont présents du à leur faible électronégativité, ce qui augmente l'interaction avec l'oxygène. Cette interaction semble être responsable de l’augmentation de la vitesse de réaction de C3H6. Les résultats NO-TPD ont montré que la forte basicité ces impuretés entraînait une plus forte adsorption du NO. Par DRIFT il a été aussi montré que l’adsorption des intermédiaires du NO, associée au champ électrostatique créé par ces cations, empêche l'oxydation de NO. L'adsorption de CO a été favorisée, améliorant la conversion du CO. La formation de phosphate de cérium observée pourrait stabiliser l'état d'oxydation de Ce3+ (vérifié par XPS), en diminuant l'oxydation de NO due au blocage des sites catalytiques. Néanmoins, les co-oxydations de CO et de C3H6 ont été améliorées en évitant l'auto-empoisonnement. Après vieillissement hydrothermal, l'effet des impuretés a été masqué par le frittage de Pt/Pd, ce qui diminue les performances catalytiques / The more restrictive regulations to reduce pollutants emissions, especially CO2, promote the use of biofuels. However, biodiesel contains inorganic elements (Na, K, Ca and P) that reduce the durability of the after-treatment catalysts. This work aims to evaluate the performance of Diesel Oxidation Catalysts (DOCs, PtPd/CeZrO2/La-Al2O3 reference catalyst). The characterization results have shown that the above-mentioned impurities affect the physico-chemical, redox, surface and catalytic properties. Although the catalyst crystalline structure of reference catalyst did not change after impurities incorporation, the specific surface area decreased. The redox ability was also decreased when Na, K and Ca impurities are present due to their low electronegativity, which increased the oxygen interaction. This high interaction seems to be responsible of the enhanced C3H6 reaction rate. NO-TPD results evidenced that the high basicity of Na, K and Ca impurities resulted in an increase of NO adsorption strength. Accordingly, DRIFT results showed the presence of NO intermediates adsorption associated to the electrostatic field created by these cations, hindering NO oxidation. CO adsorption was also promoted, enhancing CO reaction rate. The formation of cerium phosphate was also observed, which could stabilize the Ce3+ oxidation state (checked by XPS), decreasing NO oxidation due to the blockage of catalytic sites. Nevertheless, CO and C3H6 co-oxidations were enhanced by avoiding self-poisoning. After catalyst hydrothermal aging, the effect of impurities was masked by the sintering of Pt/Pd active sites, which decreases the DOC catalytic performances

To limit the environmental impact from fuel based transport of goods and mobility, the knowledge-based improvement of the hydrothermal long-term stability of Pd exhaust catalysts is demanded. Thus, the present study evaluates the performance of hydrothermally aged Pd/gamma-Al2O3 powder catalysts on lean CO oxidation (60-200°C) in the presence of H2O, and discusses structure-activity correlations. A decline in the number of Pd surface sites is quantified with growing aging temperature (650-950°C), and correlates with the decrease in the CO oxidation activity in transient state. However, unexpected shifts in the activation energy of the steady state CO oxidation are observed for the different aging temperatures and total time on stream. The characterization of the active Pd sites of the aged and non-aged catalysts before and after the CO oxidation indicate that the oxidation state of Pd changes during the lean and wet CO oxidation. The observed trends of the oxidation state of Pd correlate with the determined variations of the activation energy, successfully elucidating structure sensitivity of the CO oxidation at temperatures of 750°C or higher, and with changing total time on stream.:1 Introduction and aims 2 Fundamentals 2.1 Emissions from combustion engines 2.2 Diesel exhaust after-treatment systems 2.3 Pd catalysts for CO oxidation 2.3.1 Characterization and CO oxidation activity of Pd catalysts 2.3.2 Mechanism of the CO oxidation on Pd catalysts 2.3.3 Influence of H2O on the CO oxidation on Pd catalysts 2.3.4 Structure sensitivity of the CO oxidation on Pd catalysts 2.4 Thermal and hydrothermal aging of supported Pd catalysts 2.4.1 Sintering and phase transformations of γ-Al2O3 2.4.2 Sintering of Pd in supported catalysts 2.4.3 Kinetic modelling of the CO oxidation on aged Pd catalysts 3 Materials and methods 37 3.1 Preparation of the Pd/γ-Al2O3 catalyst 3.2 Hydrothermal aging of the catalyst 3.3 Performance of the catalytic CO oxidation 3.3.1 Temperature-programmed CO oxidation 3.3.2 Steady state CO oxidation 3.4 Characterization of the catalysts 3.4.1 N2 physisorption 3.4.2 Temperature-programmed desorption of H2 3.4.3 Scanning transmission electron microscopy 3.4.4 X-ray diffraction 3.4.5 X-ray photoelectron spectroscopy 4 Results and discussion 4.1 Transient CO oxidation activity of the non-aged and aged Pd/γ-Al2O3 catalysts 12 Contents 4.2 Quantification of the active sites of the non-aged and aged Pd/γ-Al2O3 catalysts 4.2.1 Number of Pd surface sites 4.2.2 Pd particle sizes 4.2.3 Pd crystallite sizes 4.2.4 Content of surface Pd 4.2.5 Comparative discussion of the quantification of the active sites 4.3 Investigation of the aging mechanism of the Pd/γ-Al2O3 catalysts 4.4 Steady state CO oxidation kinetics of the non-aged and aged Pd/γ-Al2O3 catalysts 4.4.1 Activation energy of the steady state CO oxidation and discussion of structure sensitivity 4.4.2 Dispersion of Pd after the steady state CO oxidation 4.4.3 Oxidation state of Pd after the steady state CO oxidation 4.4.4 Comparative discussion of the transient and steady state CO oxidation activity 4.5 Summarizing discussion of the structure-activity correlations of the nonaged and aged Pd/γ-Al2O3 catalysts for CO oxidation 5 Conclusions and outlook Bibliography List of Figures List of Tables A Annexes